The present invention relates to an improved slitter blade for slitting thermoplastic sheet as it exits from a sheet extrusion die.
In the manufacture of thermoplastic sheet from such thermoplastic polymers as graft ABS, polyethylene, polyvinyl chloride, polystyrene, polycarbonates and the like, a single sheet delivered by an extrusion die is often times slit or cut into a plurality of sheets. A plurality of blades are mounted on a bar which extends across the entire width of the sheet. The bar is rotated to positions and locked for the engagement and disengagement of the blades of the slitter with the sheet.
The blades are securely fastened to a blade holder and are a hazard to the operators of the sheet extrusion equipment, especially when the bar is rotated to position the blades away from their cutting position.
The object of the present invention is to provide a cutter blade which is exposed only when the blade is in the sheet cutting position and at all other times be automatically retracted into a blade housing. The blade of the present invention will automatically retract to a safe, shielded position when the blade is moved laterally for different width cuts; whenever the sheet breaks; whenever the extruder accidentally runs out of material and no sheet is moving on the line; and when production is completed and the extrusion line is shut down. The present blade retractor eliminates the hazard of an exposed blade before the operator can come in contact therewith and the retractable feature is not dependent on any action by the operator.